Steel beams in Australian construction: sections, grades, coatings, and selection

TL;DR

Structural steel in Australian construction (Class 1a houses through to Class 9 commercial) comes in four common section families: UB (universal beam, deep web for spanning beams), UC (universal column, square-proportioned for posts and columns), PFC (parallel flange channel, the volume lintel default), and SHS / RHS / CHS (hollow sections for posts, columns, and visible architectural steel). All hot-rolled sections in Australia are produced to AS/NZS 3679.1:2016, almost universally at Grade 300 (yield strength 300 MPa); hollow sections to AS/NZS 1163, typically Grade C350L0. Design sits under AS 4100:2020. The main decisions are section selection (the engineer’s call from a structural drawing), coating (hot-dip galvanised for any moisture exposure, gloss-black powdercoat for visible architectural steel, primer-only for fully internal hidden steel), and connections (welded, bolted, or end-plate). Steel beats LVL where the load or span won’t reach in timber, where fire rating drives the design (Class 2 separating walls, Class 5-9 commercial), or where the beam is also a visible architectural element. Lead time is the gating factor on most steel orders: 4 to 12 weeks from order to delivery is normal (verified 2026-05-13, InfraBuild Hot Rolled product guide).

What it is

Structural steel is hot-rolled or cold-formed mild steel supplied in standard cross-section shapes (the “section” or “profile”) at controlled tolerance and mechanical properties. The major Australian mill producers (BlueScope, InfraBuild, Liberty Primary Metals) supply through merchants and steel fabricators.

The four common section families:

Family	Code	Shape	Where used
Universal beam	UB	I-section with deeper web than UC; flanges narrower	Spanning beams (lintels, ridge beams, floor beams), where bending is the dominant force
Universal column	UC	I-section with web-to-flange ratio closer to 1:1	Columns and posts, where axial compression is dominant
Parallel flange channel	PFC	C-shape with parallel flanges	Lintels (back-to-back PFC pair is the standard lintel default), edge beams
Square hollow section	SHS	Hollow square tube	Posts, exposed feature columns
Rectangular hollow section	RHS	Hollow rectangular tube	Posts, lintels in narrow walls, feature steel
Circular hollow section	CHS	Hollow round tube	Decorative posts, feature columns
Equal angle	EA	L-shape with equal legs	Bracing, edge support, lintel angle iron
Unequal angle	UA	L-shape with unequal legs	Specialist supports, fascia and gutter brackets

Sections are designated by nominal depth (or side dimension) and mass per metre: a “250 UB 25.7” is a Universal Beam, 250 mm nominal depth, 25.7 kg/m. The “31.4” or “37.3” suffix after “250 UB” indicates a heavier variant of the same section depth with thicker flanges and web.

Grades

The Grade label gives the minimum yield strength in MPa.

Standard	Grade	Yield strength (MPa)	Where used
AS/NZS 3679.1	300	300	Default hot-rolled steel; UB, UC, PFC, angles
AS/NZS 3679.1	350	350	Specifier or commercial sections; less common in light framing
AS/NZS 1163	C350L0	350	Cold-formed hollow sections (SHS, RHS, CHS); the L0 designates low-temperature impact resistance
AS/NZS 1163	C450L0	450	High-strength hollow sections; rare in light framing

Grade 300 dominates hot-rolled work in low- and mid-rise construction; C350L0 dominates hollow-section use. The engineer’s drawing specifies the grade; ordering a different grade is a non-compliance even if the section dimensions match.

Standard sizes

Section	Typical range (low- and mid-rise)	Notes
UB	150 UB through 460 UB depths	200 UB and 250 UB are common lintel sizes; 310 UB and above for longer spans
UC	100 UC through 310 UC	150 UC and 200 UC dominate posts and short columns
PFC	75 PFC through 380 PFC	150 PFC, 200 PFC, 250 PFC are typical lintel sections (often back-to-back pairs)
SHS	50 × 50 through 200 × 200	100 × 100 and 150 × 150 dominate post selection
RHS	50 × 25 through 250 × 150	Architectural posts and lintels in narrow walls
CHS	60.3 mm through 273 mm OD	Decorative posts and feature columns

Standard mill lengths are 9, 10.5, and 12 metres. Sections cut to length by the supplier or fabricator are typically charged the full mill length less drop-off credit.

Where steel is the right call

Spans that exceed solid timber and engineered timber capacity: opening over 4 m wide with two-storey load over, garage door headers over 5 m, beams where deflection limits would force an oversized timber section. Steel is materially stiffer and shallower for the same capacity.

Fire-rated structural elements: NCC Class 1a houses rarely require FRL-rated structural elements; Class 2 apartment separating walls and Class 3-9 commercial frequently do. Steel can be designed to FRL-90 or higher with proprietary fire protection coatings or boxed-in plasterboard.

Visible feature steel: industrial-style architecture, exposed columns and beams in living areas, factory-warehouse-aesthetic conversions. PFC, SHS, and RHS sections finished in gloss black powdercoat or hot-rolled-and-sealed are standard architectural steel choices.

Connections to existing structures in renovation work: where the existing structure is steel or where load transfer to new steelwork requires a steel-to-steel bolted or welded connection.

Termite-vulnerable footing systems: subfloor framing in termite-active areas where chemical-treated timber is being avoided. Steel is termite-immune by definition.

Where steel is wrong

Routine residential lintels under 3 m where LVL covers the load: LVL is cheaper, faster to order, easier to fix, and reaches the typical 2.4 to 3.6 m lintel spans without engineer involvement.
Direct exterior exposure without coating: bare or primer-only steel rusts in months of weather exposure. Hot-dip galvanise or paint to a robust system; never leave external steel unprotected.
Hidden steel in residential where the carpenter can’t easily fix to it: bolting into steel requires drilling and tapping, or welded studs at the fabricator. Specifier-led steelwork sometimes lands on site with the connection points wrong for the surrounding timber framing.
Architectural steel within 1 km of coast without marine-grade coating: standard hot-dip galvanising rates at 6 to 25 years to first maintenance depending on coating thickness; marine exposure shortens this materially. Use heavier galvanising or duplex (galv + paint) for coastal exposed steel.
Where lead time matters more than capacity: steel orders take 4 to 12 weeks. LVL is typically next-day at the merchant.

Sizing and engineer’s design

Steel structural members are always engineer-designed under AS 4100:2020. There are no equivalent generic “AS 1684 span tables” for residential steel.

The engineer’s drawing specifies:

Section type and size (e.g. “250 UB 31.4”)
Grade (e.g. “Grade 300”)
Coating (e.g. “Hot-dip galvanised to AS/NZS 4680, 600 g/m2”)
Connection details (bolted, welded, end-plate, base plate)
Bearing requirements (how the steel sits on supporting structure)
Fire protection (if FRL-rated)

The fabricator works from the engineer’s drawing and produces a shop drawing detailing every cut, hole, weld, and surface treatment. The shop drawing should be checked by the engineer before fabrication begins.

Coatings

Coating	Where used	Typical service life
Hot-dip galvanised (AS/NZS 4680)	Any moisture exposure: external, subfloor, splash zones	25 to 50 years to first maintenance, exposure-dependent
Powdercoat over galvanised (duplex)	Visible external architectural steel	30+ years before recoat
Powdercoat over primer (single-coat)	Internal visible architectural steel	15 to 25 years depending on environment
Red oxide primer only	Internal hidden structural steel (boxed in or plasterboard-clad)	Service life of the building, no maintenance required
Mill scale only (no coating)	Never acceptable in service: only for storage and transport	n/a
Marine-grade hot-dip galv + duplex	Coastal exposed steel within 1 km of surf	25 to 40 years to first maintenance

Hot-dip galvanising requires the fabrication to be completed before galvanising (welds inside the galvanising pool are not acceptable). On-site cuts or modifications to galvanised steel must be repaired with cold-galv paint to restore the protective coating at the damaged area.

Connections

Steel-to-steel and steel-to-timber connections are the highest-risk part of residential steel work because errors here are difficult to remediate after fix.

Connection	Where used	Notes
Bolted end plate	Beam-to-column, beam-to-beam	Standard high-strength friction-grip bolts; engineer specifies size and grade
Welded	Fabricator’s shop, not site (general rule)	Site welding requires a qualified welder and inspection per AS/NZS 1554
Base plate bolted to footing	Column to concrete footing	Cast-in bolts or post-installed chemical anchors; engineer’s detail required
Joist hanger / face plate	Timber joist or rafter to steel beam	Proprietary timber-to-steel connector or welded steel angle
Through-bolt timber to steel	Timber top-plate sitting on steel beam	Pre-drilled holes per the engineer’s drawing; routine on lintels

The most common defect: holes drilled by the fabricator land in the wrong place for the timber framing or for the connection to the next steel member. Always check shop drawings against the engineer’s design and against the timber framing layout before fabrication starts.

Common defects and on-site issues

Wrong section delivered: a 250 UB 25.7 ordered, a 250 UB 31.4 delivered. They look identical but mass differs; check the rolling mark before fixing.
Coating damaged in handling: hot-dip galv damaged by chains during transport. Cold-galv paint to restore the coating at the damaged area before final fix.
Site welds without inspection: any field weld on structural steel must be inspected by a qualified welder per AS/NZS 1554; site welds on the engineer’s drawing are usually identified and budgeted at design time.
Wrong-grade fasteners: standard hardware-store bolts substituted for engineer-specified high-strength structural bolts (Class 8.8 or 10.9). Bolted connections under load fail catastrophically with wrong-grade fasteners.
Cast-in bolt position wrong at footing: column base plate doesn’t match cast-in bolt pattern. Either move the base plate (rare; usually impossible) or chemical-anchor the column to footing.
Steel sitting in standing water or wet concrete: subfloor steel sitting in water or with wet concrete spilled on it during pour. Even galvanised steel corrodes faster in standing water with concrete alkalinity.
Carpenter drilling random holes through structural steel: a 12 mm hole through a 200 PFC web reduces the section’s web shear capacity. Engineer review required for any hole the engineer didn’t specify.

Pricing (2026 indicative, ex-GST, ex-Sydney metro fabricator)

Section / coating / length	Per metre or item
200 UB 25.4 (Grade 300, primer)	$90-130/m
250 UB 31.4 (Grade 300, primer)	$130-180/m
200 PFC 22.9 (Grade 300, primer)	$75-110/m
150 × 150 SHS (Grade C350L0, primer)	$90-130/m
Hot-dip galv premium	+$25-50/m or 30-40% over primer
Powdercoat premium	+$15-30/m
Engineer-designed lintel beam (300 UB end-plated, supply + fabrication)	$1,200-2,800 per beam
Shop welded steel column (3 m, base plate, cap plate, galvanised)	$400-900
Site delivery (small load)	$250-500
Crane / hiab on-site lift	See crane / hiab operator

The fabrication and coating components often exceed the raw steel cost. A galvanised, end-plated, supply-and-deliver steel lintel for a residential garage opening is typically $1,500 to $2,500 in 2026 ex-GST.

Standards and references

Standards Australia, AS/NZS 3679.1:2016 Structural steel, Part 1: Hot-rolled bars and sections. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS/NZS 1163:2016 Cold-formed structural steel hollow sections. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS 4100:2020 Steel structures. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS/NZS 4680:2006 Hot-dip galvanised coatings on fabricated ferrous articles. https://store.standards.org.au (verified 2026-05-13).
InfraBuild, Hot Rolled and Structural Steel Products Catalogue (Edition 9). https://www.infrabuild.com (verified 2026-05-13).
Australian Building Codes Board, NCC 2022 ABCB Housing Provisions (steel structural references). https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions (verified 2026-05-13).